During normal development of an organism, cells migrate from their original location to form specific organs, to populate stem cell niches and to form the complex nervous system. Abnormal cell migration is also observed in invasive cancer situations. In order to reveal the underlying mechanisms of cell migration, model systems such as the Drosophila ovary have been important in the past. Nevertheless, many questions about the regulation of cell migration are still unresolved, and this proposal addresses the role of a novel factor, Rickets, that we have found to be important for normal border cell migration in the Drosophila egg chamber. Rickets encodes a G-protein coupled receptor, and we have observed that border cells mutant for rk often fail to reach their destination at the anterior end of the oocyte. This proposal aims to investigate the underlying molecular causes of the migration defects and to understand the pathway in which Rk acts to promote cell migration. In Aim 1, I will identify the cellular architecture that is altered in the mutant cells. This will involve testng the level and distribution of important cell adhesion regulators, such as E-cadherin and Beta-Catenin, and polarity markers such as PAR-1 and PAR-3 in the mutant cells. I will also test whether Rk affects JAK/STAT signaling. In Aim 2, I will perform live imaging approaches to determine precisely what aspect of cell migration is altered in the mutant cells. I will focus on te transition of the border cells from epithelial to migratory morphology, on the detachment of the cells from the epithelium, on the speed and actual motion of the cells during migration (tumbling versus running) and on the extension of actin rich protrusions from the migrating cells. I will als test whether PKA and cAMP are acting downstream of Rk in the border cells. In Aim 3, I will test whether the effects or Rk on migration can also be observed in mammalian tissue culture. For this I will use an established system of breast cancer-derived cells that can be manipulated by RNAi approaches. A previously described scratch assay will allow me to determine whether mammalian cells with knockdown levels of Rk exhibit the same defects in migration as the mutant border cells in Drosophila. The proposed work will therefore define a new input into cell migration in Drosophila, and provide novel insights into this important developmental mechanism that are relevant to human development and disease.